Fluid coking process



Dec. 3, 1968 M. E. OLDWEILER 3,414,504

FLUID COKING PROCESS Filed Oct. 27, 1966 PATENT ATTORNEY United States Patent O 3,414,504 FLUID COKING PROCESS Morey E. Oldweiler, Whippany, NJ., assignor to Esso Research and Engineering Company, a corporation of Delaware Filed Oct. 27, 1966, Ser. No. 590,083 1 Claim. (Cl. 208-53) ABSTRACT OF THE DISCLOSURE The present disclosure relates to a fluid coking process wherein secondary air is added to a flue gas containing entrained coke particles whereby the CO is combusted to CO2 and at least a portion of the coke solids are combusted. The heat of the combustion from the secondary air induced combustion is utilized to heat the entrained coke particles which are returned to the coking zone. Pollution control benefits are obtained due to lower concentrations of CO and entrained coke particles released to the atmosphere.

This invention relates to liuid coking of high boiling hydrocarbon oils and more particularly relates to recovery of heat from the flue gas or combustion gases leaving the fluid bed burner or heating zone.

According to the present invention, the fluid coke burning step is modified and improved to recover additional heat from the flue gas and entrained fluid coke particles leaving the conventional dense uidized bed burner.

In conventional fluid coking units where the fluid coke burner is operated at a temperature in the range of about 1100 F. to 1200 F. by passing primary air up through the dense fiuidized bed, the flue gas leaving the fluidized bed has a CO2/CO ratio varying from 1 to 5 with the average about 3.

According to the present invention, heat is recovered from the flue gas leaving the dense uidized bed in the burner by introducing secondary air into the transfer line burner or the gas outlet line leading from the top of the burner to preferentially burn the CO gas and heat the liue gas and the entrained coke particles to a temperature above about 1200 F. The CO2/CO ratio is increased. The so-heated coke particles can be returned to the fluid coking reactor to supply some of the heat of coking so that the airv going to the fluid bed burner may be reduced for a given heat requirement and less coke is burned so that recovery of product coke is increased.

The heated coke particles separated from the effluent from the transfer line burner can be used to maintain the fluid bed coking reactor outlet superheated to prevent or minimize carbon deposition on the equipment. Or these heated coke particles 'may be used in a first-stage transfer line reactor for high temperature short time reaction with the efuent from th-e transfer line reactor discharging into the uid bed coking reactor to supply heat thereto or returned to conventional coker bed in the usual manner to supply heat. l

By using excess secondary air, i.e., more than enough to burn the CO to CO2, some coke will be burned and the smallest particles will be burned preferentially. These small particles are most easily lost from the system and are the cause of air pollution. Thus, preferentially burning them reduces air pollution.

According to this invention, two-stage coke burning is used in a fluid coking process to burn some of the relatively low temperature uid coke product from the fluid ice coking reactor and heating them to an elevated temperature by introducing secondary air into the effluent or outlet pipe from the top of the fluid bed burner or heater to burn the CO substantially completely to CO2 and with the option of burning some additional coke to obtain even higher temperatures, more heat, or reduce pollution without the need for adding any auxiliary fuel.

With the present invention the air requirement for the uid bed burner is kept at a minimum and product coke is increased by the substantially complete combustion achieved.

The fluid coking process is a well-known process and is disclosed in Pfeiffer et al. Patent 2,881,130, granted Apr. 7, 1959. The fluid coking process is used to crack petroleum residues to make gas oil that is useful as a feed stock for catalytic cracking. In these cases the residual oil is recovered as bottoms in a pipe still operation which may be an atmospheric pipe still and/ or a vacuum pipe still.

In the fiuid coking process a heavy residuum oil is injected into a reactor or coking vessel containing a dense uidized turbulent bed of hot finely divided solids, such as coke particles. The heat of cracking or coking the heavy oil is supplied by withdrawing solids from the coking vessel, heating them and returning the heated solids to the coking vessel.

Heat is supplied in the conventional fluid coking process by withdrawing coke particles from the coking vessel and burning a part thereof in a burning or heating vessel to raise the temperature of the coke particles about F. to 200 F. higher than the temperature in the coking vessel and then returning the so-heated coke particles to the coking vessel.

In the coking of heavy hydrocarbon oils, such as heavy crudes, atmospheric and vacuum still crude residua, tars, pitches, etc., either for the production of fuel products, such as gasoline and gas oils, or for the production of chemical raw materials, such as aromatics and olefins, one of the major by-products is petroleum coke. Typically, such feeds can have an initial boiling point of about 700 F. or higher, an API gravity of about 0 to 20, e.g., 1.9", and a Conradson carbon content of about 5 to 40 weight percent, e.g., 30 weight percent. The amount of coke formed depends on the character of the materials being processed and, to some extentupon the coking conditions. In the case of high Conradson carbon stock, such as residuum from Hawkins crude, the coke yield can be 20 weight percent or higher 0n the residuum. Other stocks have been found wherein the yield can be as high as 35 weight percent. The coking of other hydrocarbon feeds, both liquid and gaseous, may be accomplished in a similar manner.

The fluid coking unit consists basically of a reaction vessel or coker and a burner vessel. In a typical operation, the heavy oil to be processed is injected into the reaction vessel containing a fluidized bed of inert solid particles, preferably coke particles, maintained at a temperature in the range of 850 F. to 1200D F., and preferably at 900 F. to 1100 F., for the production of fuels, or at a higher temperature, eg., 1200 F. to 1600 F., for the production of chemicals, i.e., aromatics and oleiins. Uniform temperature exists in the fluidized coking bed. Uniform mixing in the fluidized bed results in virtually isothermic conditions and effects rapid decomposition of the feed stock. In the reaction vessel or coker, the feed stock is partially vaporized and partially cracked. Product vapors are removed from the coking zone and sent to a fractionator for the recovery of gas and light distillates therefrom. Any heavy bottoms is usually returned to the coking zone.

The coke produced in the process remains in the bed coated on the solid particles thereof.

The heat for carrying out the endothermic coking reaction is generated in the burner vessel. A stream of coke or coke-coated, solid inert particles, if the latter are used, is transferred from the reaction vessel or coker to the burner vessel employing a standpipe and riser system, air being supplied to the riser for conveying the solids to the burner. Heated coke is then returned to the reaction vessel, usually by means of a standpipe and control valve, thereby completing the cycle.

Suflicient coke or carbonaceous matter is usually burned with an oxygen-containing gas in the burning vessel to bring the solids therein up to a temperature suicient to maintain the system in heat balance. The burner solids are maintained at a higher temperature than the solids in the reaction vessel. About 5% of coke on the feed is burned for this purpose. This amounts to approximately to 30% of the coke made in the process. The unburned portion of the coke represents the net coke formed in the process. This coke is preferably withdrawn from the burner, normally cooled and sent to storage. The coke normally contains about 86% to 94% carbon, 1.5 to 2% hydrogen, 0.5% to 7.5% sulfur, 0.6% to 1.5% volatile matter at 1100 F., up to 6% volatile matter at 950 C., and approximately 0.1% to 1.0% ash.

The method of fluid solids circulation described above is well known in the prior art. This solids handling technique is described in greater detail in Packie Patent 2,589,124, issued Mar. 11, 1952.

In the drawing, the ligure diagrammatically represents one form of apparatus adapted to carry out the invention, but other forms of apparatus may be used.

Referring now to the drawing, the reference character 10 designates a line for introducing the heavy petroleum oil feed into a cylindrical coking vessel or reactor 12 which contains a fluid dense turbulent bed 14 of solids having a level indicated at 16. The oil feed is preferably introduced directly into the uid bed 14 which is at a conventional fluid coking temperature of between about 850 F. and 1200 F. and preferably between about 900 F. and 1l00 F. for coking operations where gas oil and middle distillates are desired. Where higher temperatures are desired to produce unsaturated gaseous hydrocarbons and aromatic hydrocarbons, the temperature in the coking vessel may go as high as 1300 F. to 1800 F.

The iluid coke or inert particles in the uid bed 14 have a particle size in the range of about 70 to 600 microns with a preferred average size range between about 100 and 300 microns. Preferably not more than about 1.0% has a particle size above about 600 microns and about 5 to 40% of the particles have an average size between about 40 and lf25 microns. These finer particles are helpful in improving uidization of the lluidized bed and the circulation of solids through the unit.

The oil feed in line 10 is preferably preheated by conventional means to a temperature between about 600 F. and 800 F. During the coke operation, a portion of the oil feed is converted to coke which is deposited on the fluidized solid particles in the coking vessel 12. The rest of the oil charge is converted to gas andnormally liquid distillate hydrocarbons.

The inert or coke solids in coking vessel 12 are maintained as a dense tluidized bed 14 by vapors and steam passing upwardly through the dense bed 14. The vapors are formed by coking the oil feed. The steam is introduced into the bottom of vessel 12 through line 18 for upward passage through the fluidized bed 14. The average supercial velocity of the rising or upflowing gaseous material in the coking vessel 12 is preferably maintained between about 0.5 and 3.0 feet per second, depending on the size of the particles making up the bed.

During the coking operation as above pointed out, coke is deposited on the coke particles formed in the dense iiuidized bed and the particles continue to grow and some means must be provided to supply iine solid or seed particles to the dense liuidized bed to maintain the uidized condition. To maintain the desired amount of solids in the unit and of the desired particle size range, it is necessary to replace the coarser particles with finer coke particles. This may be done by withdrawing some of the larger particles, grinding them and returning the ground particles to the other vessel 22 or the burner vessel hereinafter to be described. The preferred method is to use a high velocity jet of steam which impinges on the coke particles in the bed and causes them to attrit and form small particles.

The products of coking and steam pass up from the dense iluidized bed and entrain coke particles therewith above the dense bed 14 and into the dilute phase 22. The gaseous products containing entrained coke particles are passed to the inlet 24 of cyclone separator 26 preferably arranged within the upper part of the coking vessel 12. The cyclone separator 26 may include a plurality of cyclone separators. The cyclone separator 26 has a diplcg 28 for returning separated solids to the dense uidized bed of solids 14 in the coking vessel 12. The separated hot converted vapors and gases pass out through cyclone separator outlet line 32 and are sent to a fractionator (not shown) to recover desired products.

As pointed out above, coke is deposited on the fluidzed particles during the coking step and to supply the heat of coking, the coke particles are withdrawn preferably continuously directly from the dense uidized bed 14 through line or standpipe 34 and mixed with steam introduced into line 34 through line 36 and the resulting suspension is passed through line 37 and introduced above air distributor of burner or heater vessel 38 which is a vertically arranged cylindrical vessel. The burner vessel is at a teniperature between about l000 F. and 1500 F., preferably between about 1100 F. and 1400 F.

In the burner vessel 38 part of the coke particles are burned to raise the temperature of the coke particles which are to be returned to the coking vessel to supply heat thereto. Air for burning the coke is Preferably added to the bottom portion of the burner vessel 38 through one or rnore lines 42. The air then passes through a distributor into the bed. During the burning and heating of the coke particles in heater vessel 38, the coke particles are maintained as a dense fluidized turbulent bed indicated at 44, having a level at 46.

Heated coke solids are withdrawn continuously from the dense fiuidized bed 44 through line 48 and returned to uidized bed 14 in the coking reactor or vessel 12. Excess coke particles are withdrawn as product coke through line 49.

In the burner or heater vessel 38 there is also a dilute phase or suspension 52 above the dense phase level 46. Combustion or flue gases pass upwardly through the burner vessel 38 at a superficial velocity between about 0.5 and 6 ft./sec., preferably 2 to 6 ft./sec., to maintain the coke as the dense uidized bed 38. The liue gases leaving the fluidized bed 38 contain entrained coke solids. In the specic form of the invention shown in the drawing, the cyclone separation system is not located within the top of the burner Vessel as it is in the conventional iiuid coke unit, but is located externally of the burner vessel at 54.

The cyclone separation system 54 preferably comprises a plurality or series of cyclone separators. The ue gases containing entrained coke liuid solids leave the top of the burner vessel through line 56 and pass into the cyclone separator system 54 to separate coke solids from hot combustion or flue gases. The present invention is also useful in conventional fluid coking units where the cyclone separation system is located internally of the burner vessel at the top thereof, similarly to that shown in the coking vessel 12.

In the conventional fluid coking unit there will be less entrained coke particles in line 56 and the entrained particles will be smaller. In modifying a conventional coker heater to this type, it would be necessary to remove the cyclones from vessel 38 to increase coke flow in line 56. In addition, the dilute phase outage 52 would also probably have to be reduced, for example, by extending line 56 down into vessel 38 as one possible method, or by shortening the straight side of the reactor dilute phase. The heat in exhaust gases from line 62 can be recovered in conventional waste heat facilities like 64.

In the burner vessel 38 there is incomplete combustion of the coke particles and also at the conditions in the burner vessel 38, O2 gas reacts with the coke particles to produce both CO2 and CO gas. In addition, at higher fluid bed temperatures in burner vessel 38 the ratio of CO2 to CO is reduced by the effect of temperature on the equilibrium. The CO2 to CO ratio in burner vessel 38 varies between 1 and 5 and the average is about 3. Thus, at higher temperatures, the amount of air or oxygen must be sharply increased for a given heat release or coke burning rate. This makes it unattractive to operate conventional burner vessels at temperatures above about 1300 F.

The gas outlet line 56 leading from burner vessel 38 to cyclone separation 54 comprises a transfer line heater and in the present invention is used as a transfer line burner to burn the CO to CO2 in the flue gas leaving burner 38 and if preferred may also be used to burn some of the entrained fluid coke. The conventional transfer line coke heater or burner requires the introduction and burning of an auxiliary fuel with the introduced air in the presence of coke particles to heat the coke particles to an elevated temperature. Depending upon the coke temperature and the method of injecting the air and auxiliary fuel, the coke may or may not be burned. In the case where it is desired to use the coke as a fuel, and thus avoid the need for auxiliary fuel, the inlet coke temperature to the conventional transfer line heater must be above about 1500 F. At lower temperatures, the burning rate of the fluid coke particles is so slow that the coke particles do not have time to burn in the conventional transfer line heater.

In the present invention, secondary air is introduced into outlet gas line 56 through one or more lines S8 near the outlet from the burner vessel 38. The secondary air burns the CO to CO2 in the flue gas leaving burner 38 to release heat and this heats the entrained coke particles in the transfer line heater or gas outlet line 56. The density of the coke particle suspension in the outlet line 56 is between about 0.005 and 5 lbs./cu. ft. compared to between about 25 and 60 lbs/cu. ft. of the dense fluidized bed 44. The size of the coke particles in the dilute phase 52 or gas outlet line 56 is between about 30 and 600 mircons. One alternate would be to entrain all the circulating coke through line 56 in which case the size would be the `same as described previously; if only part is entrained, the particles would be a little finer.

By using the gas outlet line 56 as a secondary burner, there are in effect two burner vessels. The first burner 38 burns and heats coke particles which come from the fluid coker at a temperature between about 900 F, and 1300 F. The coke particles are heated to between about l100 F. and 1500 F. in the first burner vessel 38. The combustion gases leaving the burner vessel 38 have a CO2 to CO ratio between about 0.5 and 5 and a temperature between about 1100 F. and 1500 F. Secondary air is introduced into the lower portion of the gas outlet line 56 which forms a transfer line burner to burn the CO to CO2 with essentially complete combustion of the CO with oxygen in the air to CO2. No auxiliary fuel of any kind is needed. But of course there is no technical objection to it being added if more heat is needed and it is undesirable to burn coke. This is a variable that may be used in control of the temperatures and heat input to coke.

The flue gas and entrained coke particles in the second burner are heated to a temperature of between about 6 1200 F. and 2200 F. and the CO2 to CO ratio of the combustion or flue gas is between about 5/1 and 50/1. The AT on coke between vessel 38 and 76 can be designed for anything in the range of about 20 F. to 800 F. depending upon coke rate, secondary air rate, auxiliary fuel, etc.

In the cyclone separation system 54 heated coke particles are separated from hot flue gases. The hot flue gases pass overhead through line 62 to a heat recovery system 64 such as a waste heat boiler to produce steam by introducing water at 66 and recovering steam from line 68. The amount of sensible heat in the flue gases is much greater than in the conventional burner so that this increases the incentive to install heat recovery facilities. The hot flue gases leave the waste heat boiler through line 72. These flue gases will be almost entirely N2, CO2 and H2O with very little CO or O2. It thus could be used as a source of CO2 or N2 or inert gas. The steam may be used as a carrier gas in the system.

The hot separated coke particles are removed from the cyclone separation system 54 through dipleg 74 and passed to storage or collecting tank 76 provided with a gas outlet line 78. Tank 76 is not essential if coke from line 74 is going to say only one point, but if it is to Ibe sent to several points it would probably be desirable to include a reservoir tank such as 76 as a drawoff point. If included it would normally be aerated but only with a minimum amount of gas (approximately 0.1 ft./sec. or so). The hot coke particles from tank 76 are withdrawn from the bottom thereof through line 82 and passed through valved line 84 and into fluid coking vessel reactor 12 to supply some or all (with ow 48 shut olf) of the heat of coking so that less coke is burned in the burner vessel, more product coke is produced and less air is used. With the efficient coke heater described here it is economically attractive to operate coking reactors at higher than normal temperatures, that is, up to about 1300 F.

If desired, a portion of the hot coke particles from line 84 may be diverted through valved line 86 for introduction into the top portion or exit end of the fluid coking vessel 12 to superheat the coking vessel 12 exit vapors to eliminate or to reduce coke formation on equipment in this region. Instead of using the heated coke particles from lines 84 and 86, it is sometimes more convenient to withdraw partially heated coke particles from the fluid bed burner 44 and pass them through line 86 into the exit end of coking reactor 12.

In certain cases the storage tank 76 may be eliminated so that the dipleg 74 would lead directly into line 82 or where a plurality or series of cyclone separators is used the diplegs would discharge into a hopper feeding line 82.

As an alternative, the hot coke solids from line 82 may be passed through line or standpipe `88 for use in a high temperature short time coking or cracking process. Steam or the like is introduced from line 90 into the Ibottom of standpipe 88 to form a suspension of coke particles in steam and the suspension is passed into the bottom portion of a transfer line reactor 94. As yet another alternative, the hot coke solids may go directly from line 82 or dipleg 74 to the bottom portion of transfer line reactor 94. Steam from line 68 of waste heat boiler 64 may in part be used in lines 90, 36, 18, 91 and 95.

Oil feed such as gas oil, heavy naphtha and the like is introduced through line 96 into the bottom of transfer line reactor 94 where the oil is heated to a temperature between about 1200 F. and 1500 F. for a period of time of about 0.05 to 1.0 seconds to crack the gas oil to unsaturated hydrocarbons such as olefins and diolefins and aromatic hydrocarbons such as benzene, toluene, etc., which aromatic hydrocarbons can be used as such as chemicals or in motor fuels. The hot products of reaction leave the top of the reactor V94 and are passed into the bottom of the fluidized bed 14 in the fluid coker vessel 12 where they are quenched by the fluid bed 14 to a temperature between about 900 F. and 1100D F. while supplying heat to the iuid bed 14 in coking vessel 12. Alternatively, the effluent from 94 can go to a separator followed by a quench system to recover the high olens, etc. separately from vessel 12 products.

The temperature to which the coke particles are heated in the transfer line heater 56 depends on the CO2/CO ratio, the quantity of ue gas leaving burner vessel 44 and passing into heater 56, the coke iiow through heater 56, and the amount of secondary air introduced through line 58. The CO2/CO ratio is controlled by varying the temperature of the uid bed 44 in burner vessel 38. This is done by varying the air rate in line 42 and/or the coke rate 37. The ratio and quantity of both primary air and secondary air is also controlled to give the desired outlet coke temperature from transfer line heater 56. The ratio of air rate 42 to coke rate 37 iixes the temperature of bed 44 and the CO2/CO ratio; increasing air increases temperature of 44. Part of the coke may be drawn off bed 44 through line 48 at the desired temperature and rate. All or the remaining amount of coke goes up line 56 and may be heated by adding at least enough air to burn all CO to CO2. This fixes the temperature and rate of coke at 74. Now, if it is desired to increase the temperature of coke at 74, it is possible to add more secondary air and burn up coke as well as the CO or reduce coke rate 37 and with total air constant shift more air to the secondary inlet. The temperature in 44 should stay the same and the temperature of 74 go up with same total heat going into the coke. If it is desired to increase total heat to coke, one must use more total air and by keeping the ratio of primary to secondary air the same one can increase the temperature of yboth 44 and 74 coke.

The transfer line heater S6 can be between 10 feet and 50 feet long and can operate with superficial gas velocities in the range of to 150 ft./sec.

In another application yof the present invention, the hot gas and coke particles from line 74 or 82 could be used to supply all the heat or part of the heat of calcination of the product coke withdrawn through line 49. If line 74 is being operated at a temperature `of at least 1700 F. to l800 F., this coke will already be calcined and product can be drawn off vessel 76 through line 50.

In the present invention the amount of primary air introduced via line 42 into fluid bed burner 38 is between about 1000 and 5000 s.c.f. per barrel of oil feed to the fluid coker 12. The amount -of secondary air introduced into the bottom portion of the second or transfer line burner 56 is between about 200 and 1500 s.c.f. per barrel.

Using a modified coker with fresh total feed rate of 14,000 b./d. as the basis, the coke particles in bed 44 are at a temperature of about 1300" F., the air rate 42 is 25,300 s.c.f.m., the quantity of ilue gas leaving the bed burne-r 44 is about 55,000 actual c../min. and the flue gas contains entrained coke particles having a density of about 0.06 lb./cu. ft. and a CO2/CO ratio of 1/1; it is found necessary to introduct 8,350 s.c.f./min. of secondary air through line 58 to heat the entrained coke particles to a temperature of about 1800" F.

In a specific example of the present invention where hot coke solids from transfer line burner 56 are introduced into a 30 foot long transfer line reactor 94 to carry lout a high temperature coking operation as a feed to 94 2,000 bbl/day of a gas oil at 600 F. having an API gravity of and an average boiling point of 700 F. with reactor 94 operating at l400 F. and 1.6 tons/min. of 1800 F. coke flowing to reactor 94 with a velocity of 80 ft./sec. and a density of 0.15 lb./c.f. coke and a 0.4 second residence time inside reactor 94. An oil feed of 12,000 barrels a day of petroleum residuum having an initial boiling point of about 950 F., an API gravity of 6 and a Conradson carbon of 20 weight percent is introduced into coking reactor 12 which has a coke holdup of about 225 tons of iluid coke particles, mostly of a size between about .100 and 300 microns. The temperature of the resid- 8 uum feed is 700 F. and the temperature of the uid bed 14 in reactor 12 is 1000 F. The density of the coke in fluid bed 14 is 40 lbs/cu. ft. The superficial velocity of the gaseous material passing up through reactor 12 is 1.5 ft./ sec. average.

The circulation rate of coke particles between the fluid coker 12 and uid burner 38 is 4.6 tons per minute.

Coke particles passing through line 37 from reactor 12 are introduced into the bottom portion of fluid bed burner 38 where the temperature of the iiuid bed 44 is l300 F. The coke holdup in burner vessel 38 is 75 tons. The amount or quantity of air at ambient temperature introduced into burner 38 through line 42 is 25,300 s.c.f. per minute. The density of the fluid bed 44 is 40 lbs./ cu. ft. The CO2/CO ratio of the flue gas leaving burner 38 outlet and entering transfer line heater 56 is l/ l. The density of solids in this flue gas in heater 56 is 0.06 lb./cu. ft. The superficial velocity of the gaseous material passing up through burner vessel 38 is 2.5 ft./sec. The amount of coke particles recovered in separation means 54 is 1.6 tons/min. To increase the temperature of the flue gas in transfer line burner 56 by burning CO and also to heat the entrained coke particles, 8,350 s.c.f. per minute of secondary air at ambient temperature are introduced into the lower portion of burner 56 through line 58.

The temperature of ilue gas and entrained coke particles at the outlet of Ireactor 56 is 1800D F. About 1.6 tons per minute of heated coke particles are recovered by the cyclone separator system 54 and this amount of coke particles is passed through lines 82 and 88 and introduced into coking reactor 94 to supply heat thereto. In reactor 94 the coke is cooled to l400 F. while heating feed 96 from 600 F. to 1400 F. and cracking it. The coke and cracked feed issuing from 94 enter reactor 12.

By using the coke particles and gas from reactor 94 and the coke from line 48, a temperature of 1000" F. is maintained in the reactor 12 without the necessity of burning as much coke product as previously was required so that more coke product is produced and less total air is needed for heating coke in the heater system, i.e., burners 38 and 56.

The amount of product coke per day obtained when using the present invention is 3500 pounds per hour more than when using a conventional fluid coking process requiring the same heat input. Also the amount of primary and secondary air used in lines 42 and 58 in the 4present invention is less by 3000 s.c.f. of air per minute.

In a conventional liuid coking unit the cyclone separation system is located inside in the upper part of the burner vessel corresponding to burner Vessel 38 as shown in the figure, In such a conventional unit the CO2/CO ratio `of the ilue gas leaving the iluid bed burner using the same temperature and conditions as given above in the example of the present invention is 3/ 1, the temperature of bed 44 is 1175 F., and the density of the flue gas leaving the fluid bed burner after having passed through the internal cyclone separation system in the uid bed burner is extremely low value of about 0.0001 lb./ cu. ft.

The process -of the present invention as represented by the conditions of the above example yields about 4250 barrels per day of naphtha having a boiling range of C4 to 430 F., about 5700 barrels per day of gas oil having an API gravity of 16, about 400 million s.c.f./ day of gas (C3 and lighter) having an average molecular weight of 2() and 13,000 tons of product coke per day. Included in the gas is 210,000 lb./hr. ethylene which is about 3 times the amount which would have been obtained with only a conventional coker.

What is claimed is:

1. A uid coking process which includes thermally cracking a heavy oil in a fluid bed reactor to produce lower boiling hydrocarbons and coke, removing coke solids from said reactor and burning at least part thereof with primary air in a fluid bed burner vessel, removing at 9 10 least a portion of the unburned coke solids as product References Cited coke, removing ue gas containing entrained coke solids and CO overhead from said uid burner, introducing sec- 'UNITED STATES PATENTS ondary air into the removed flue gas to eifect combustion 2,734,853 2/ 1956 Smith et al 208-127 of CO to CO2 thereby heating the entrained coke solids, 5 2,944,007 7 /1960 Metrailer 208 127 separating the so heated entralned coke sohds, passlng 3,162,593 12/1964 Persyn u 208 127 said heated coke solids to the inlet end of a transfer line coking zone to crack a separate stream of oil at a higher I temperature above about 1300 F. in a transfer line cok- DELBERT E' GANTZ Primary Exammer ing zone and discharging the reacted mixture from Said 10 H. LEVINE, Assistant Examiner. coking zone into said fluid bed reactor. 

